Make Nitric Acid - The Complete Guide


Uploaded by NurdRage on 03.06.2009

Transcript:
Greetings fellow nerds.
Nitric acid is an extremely useful acid
capable of dissolving copper and silver.
In this video we're going to show you three approaches to making it.
For the first method,
we start with about eighty grams of a nitrate salt.
We're using sodium nitrate
but you can also use potassium nitrate, ammonium nitrate,
or even a nitrate based fertilizer
as long as it passes the nitrate test
we showed you in a previous video.
Alright, add around 50 mL of water to your nitrate
and try to dissolve as much of it is as you can.
Then carefully add 100 mL of hydrochloric acid.
Give it a few minutes to settle
and in this larger container place 50mL of water.
Now place the acid mixture inside the larger container like this.
Now get at least 32 grams of copper, an excess is better,
and pour it into the acid mixture.
Now place a container large enough to fit over the inner container,
but small enough to fit inside the outer container,
into the apparatus.
And now, just wait.
The copper reacts with the acid and nitrate mixture to generate
nitrogen dioxide gas that flows out and is forced to flow into
the water where it dissolves and produces nitric acid.
This process is not very efficient but it works.
We placed this weight over the container
to keep it from bumping too much.
This took about an hour so we'll skip over that part.
Alright here we are.
Take out both inner containers.
Pour out the acid.
And here is your really weak nitric acid.
It's green because it's highly contaminated
with the original reaction mixture that splashed out.
But it's still somewhat useable.
To test it, just pour it over some pieces of copper.
Only nitric acid can dissolve copper.
Now to generate cleaner acid
use a more sophisticated gas generator
which simply consists of this vacuum flask
with a plastic tube and a glass pipette at the end of it.
Do not omit the pipette since you don't want
the acid produced getting on the tube and possibly reacting with it.
Now fill the flask with 80 grams of nitrates just like before.
Then add 50 mL of water and at least 32 grams of copper.
Do not add the hydrochloric acid yet.
Our mixture in the video is turning green
because we used recycled copper waste from our lab,
if you use clean copper this shouldn't happen.
Anyway, get a container that can fit a 25mL graduated cylinder.
Then fill the cylinder with 25mL of 30% hydrogen peroxide.
The peroxide is optional but it helps to improve nitric acid yield.
You can use water if you don't have peroxide but your yield will be lower.
Ok now pack the container with ice
and fill it with water to form a slurry.
This ice bath for the cylinder helps more of the nitrogen dioxide
dissolve and react before it escapes.
Now lead the gas generator output pipette into the graduated cylinder.
Ok when you're ready to start,
pour 100mL of hydrochloric acid into the gas generator
and stopper it off.
And there goes the reaction.
This took about an hour to finish so we'll skip ahead.
Now simply take apart the apparatus and get your acid.
And here it is, still dilute,
but stronger than the other method and very clean.
You can test the acid by pouring it over copper.
Now we can't predict the concentration of the acids you'll obtain
because everyone's setup will be slightly different.
But if you want highly concentrated acid
you can distill the acids by fractional distillation
to obtain an acid of 70% concentration.
You cannot go higher because nitric acid forms an azeotrope with water.
But as you can see here,
concentrated nitric acid is still extremely reactive.
Ok now for both methods lots of copper was used
but copper is pretty costly for the amount of acid you get.
But, you can actually recycle the copper to use again for more acid.
Get the dead reaction mixture and simply add aluminum metal.
This is going to produce lots of heat and hydrogen gas so be careful.
We used aluminum foil but this is actually pretty expensive,
it's cheaper to use aluminum cans that you've sanded off the labels.
Ok, keep on adding aluminum metal until no more metal dissolves.
Then take out all the extra aluminum bits and filter off the mixture.
The solid product is copper.
It's highly contaminated with aluminum metal
but still very useable to make more nitric acid.
In this final method we're going to make nearly pure nitric acid.
First get a round bottom flask and fill it with
about 50 grams or so of a pure nitrate salt.
Do not use impure fertilizer for this.
Get your condenser ready to for the acid.
Now add concentrated sulfuric acid to the nitrate.
We used 100mL so you could see it on camera better
but this is far too much.
You can use a stoichiometric amounts
to save on the valuable sulfuric acid.
Attach a still head with a glass stopper at the end.
You can install a thermometer if you want but this is optional.
Now get a high temperature oil bath ready
and with water in the condenser on, turn on the heat.
What's happening is the nitrate salt is reacting with the
sulfuric acid to create a sulfate salt and nitric acid
which boils out of the mixture driving the reaction forward.
The brown yellow color of the gases results
from some of the nitric acid decomposing into nitrogen dioxide,
oxygen and water from the heat.
The acid on the left is yellow due to nitrogen dioxide
contamination but this is very little.
The acid in there is actually stronger and purer
then the concentrated acid we showed earlier.
Now the whole distillation took an hour so we'll skip over that.
And here we have our nearly pure nitric acid.
It's also called fuming nitric acid for this reason,
if you blow air at it... it fumes!
Do not inhale.
Ok now something surprising about pure nitric acid
is that if you add it to copper... it actually reacts pretty slowly.
This is because the pure nitric acid is so strong
that it actually reacts with copper to form a protective layer
that resists further attack.
This process is called passivation.
But to break this effect we just add a little water
to lower the concentration of acid.
And there it goes.
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